In wireless communications systems, a slot based random access procedure may be used to initiate communications. In such systems, a pre-defined sequence such as a preamble can be transmitted in alignment with an access slot. The pre-defined sequence can be transmitted as part of a signal from a mobile unit. A base station or other network element can be configured to receive the signal from the mobile unit and detect the pre-defined sequence. The network element can be configured to coherently correlate the received signal and the pre-defined sequence over a sequence period using a detection algorithm.